Siemens SINUMERIK 840DE sl Commissioning Manual page 1354

Configuring the system
2.3 Configuration file "basesys.ini"
; PLC will happen
;DisablePLCTimeSync=1
; PLCTimeType informs time synchronization what kind of time
; is kept in PLC:
; local: PLC uses "wall clock time", with switches between DST and
;
;
;
;
;
;
;
;
;
;
;
;
; local-nodst: PLC uses local time as above, but without DST
;
;
;
;
;
;
;
;
; utc: PLC clock contains universal time (= GMT+0)
;
;
;
;
;
;
;
36
standard time, if DST exists in the selected Timezone
If Linux synchronizes to an external server and passes time on
to PLC, this means the PLC clock is changed twice a year.
For PLC time-of-day interrupts this means they can be skipped
(begin of DST) or executed twice (end of DST). If this might be
an issue,try to avoid such interrupts between 2am and 3am.
If Linux receives time from PLC, it assumes that this clock will
switch between DST and standard time somehow (manually or
automatically). If this doesn't happen (or is delayed) Linux time
will be 1h behind the correct value. NCK and drives will still
follow PLC clock.
(summertime). All components (PLC, NCK, HMI, drives) always
use standard time, even if the selected timezone has a DST.
If Linux receives time from the PLC, it assumes standard
(non-DST) time, too. If this is not the case, the Linux clock
will be 1h ahead of the correct value.
This time type has been used implicitly up to SW 4.7.3 and is
still the default to maintain compatibility.
All components (PLC, NCK, HMI, drives) will use UTC.
However, S7-300 engineering and HMI Operate 4.7 are not prepared
for displaying UTC times as local times yet.
This type makes synchronization simple, as no changes for
timezone or DST are needed. It also avoids changes to PLC clock
and supports applications across different timezones.
If Linux receives time from the PLC, it assumes UTC there.
Commissioning Manual, 12/2017, 6FC5397-1DP40-6BA1
NCU operating system